These excavation devices make excavations with substantially rectangular section in the ground, down to a depth of a few hundreds of meters. Subsequently, once the excavation tool is extracted, the excavations are filled with hardening material, e.g. cement, and possibly with reinforcing elements, such as metal cages, to obtain panels or diaphragms in the ground. These panels may have both structural functions as foundation elements or water-proofing functions. During the execution of the excavation, the excavation itself is maintained filled with stabilizing fluid which, thanks to the generated pressure, has the function of bolstering the walls of the already excavated segment, preventing them from collapsing. The stabilising fluids or slurries are generally mixtures containing bentonite or polymers. The excavation device, also known as excavation module is, then, immersed in the stabilizing fluid during the execution of the excavation.
If the excavation device is a hydromill, normally used to obtain diaphragms, in order to supply actuating power to said excavation device it is necessary to connect the latter to a series of feeder lines, comprising pipes and/or cables, e.g. hydraulic oil pipes, wires for electrical instrumentation and control, generally also inserted in feeder pipes provided with such construction features as to be compatible with the work site, in particular to be suitable to be immersed in the stabilizing fluid during the excavation. These feeder lines thus connect the excavation module to the base machine located at ground level, on which are installed devices for the generation of hydraulic and electric power, such as e.g. hydraulic pumps, endothermic engines, electric engines, batteries. The base machine may be, e.g., a crawler crane, a cable excavator or a drilling machine. The feeder lines, starting from the excavation tool, are generally wound around a drum pulley positioned at the top of the arm to which said tool is suspended and then drop towards the base machine on which they are collected and accumulated. The feeder lines must follow the descent and rise movement of the excavation device within the excavation, thus being immersed in the stabilizing fluid. In order for the feeder lines to be maintained in an orderly position during the movement of the excavation tool, said feeder lines are wound around a rotating drum of a winder, generally installed on the base machine, which, rotating, winds them or unwinds them according to the necessary movements required by the excavation. The feeder lines are then deposited on the drum of the winder, accumulating on multiple superposed layers or coils, so that each new outer layer is wound with a greater radius of curvature than those already wound, which are closer to the rotation axis of the drum. Because of their weight, when the line feeder tubes are wound around the drum of the winch, each coil is subjected to strong pressures generated by the weight of all the subsequent outer coils, superposed on it. This causes the innermost coil, the one wound directly on the drum, to be the one subjected to great pressures. When the depths of the excavation are significant, indicatively more than 100 m, the length and the weight of the feeder lines have considerable values, and this can create excessive loads and stresses on the lines themselves, both on the segment unwound from the drum and suspended from the arm of the base machine, and on the segment still wound on the drum of the winder.
For the segment of the feeder lines unwound from the drum, it is necessary for the lines to be guided and supported, to prevent them from becoming entangled during the rise and descent in the excavation, as well as to enable them to correctly slide on the drum of the pulley positioned at the top of the supporting arm, and to prevent an excessive pulling force, generated by their own weight, from creating excessive elongations of the tubes or cables, causing, in some cases, undesired breakages. In fact, if the tubes or cables are too elastic, the moving system may not be able to respond in a timely manner to the winding and unwinding commands, imparted by the drum of the winch, causing problems in the correct winding. It is thus necessary to relieve the feeder lines of at least a part of the effect of their own weight, connecting them to support and guiding elements, which are structured to bear the weights without causing deformations or elongations of the lines themselves. In fact, merely increasing the thickness of the feeder tubes to boost their load-bearing capacity would reduce their flexibility and this would not enable them to be wound sufficiently fast on the drum. Hence, it is necessary to bind the feeder tubes to each other, so they can be wound in an orderly manner, as well as to fasten them to appropriately structured support and guiding elements, so that in the segment of the feeder lines that is wound on the drum are said support elements to bear the loads generated by the weight of the wound layers of tubes, relieving the tubes themselves of these loads, so that they do not undergo structural damages, such as crushing. Moreover, the support and guiding elements must prevent entanglements between the feeder pipes themselves during their movement.
From European patent EP0518292, an excavation device is known, e.g. a hydromill, wherein the feeder tubes are kept distanced from each other, in parallel, by transverse bars, also called crossbars, fastened along the tubes at regular intervals: these bars are maintained at the proper distance from each other, in longitudinal direction of the tubes, by appropriate shaped spacers, creating two support branches positioned laterally to the tube.
The terminals of the crossbars and the shaped spacers are traversed by a support cable for each branch. In particular, the spacers have a hole that allows the passage of the cable, letting the spacers be axially slidable with respect to the cable. The shaped spacers are interposed between two consecutive bars, during the assembly of the feeder lines, in an adequate number to fill the entire space present between the two bars, in such a way as to maintain said bars at the desired distance. During said assembly step, the support cables are not subjected to external loads.
When the feeder lines are extended within the excavation, the entire weight of the pipes and of the space elements bears completely on the two lateral support cables. Because of the weight of the excavating module and because of the tension that is generated during the extraction of the excavating module from the fluid-filled excavation, an elongation of the support cables can occur. Because of the fact that the spacers can slide along said cables, such elongation would entail that in the segment between the tool and the transmission pulley, located in the upper region of the support arm, all spacers would tend to slide downward, leaving a segment of the cables exposed in proximity to the pulley, i.e. a segment of free cable would be created between the spacers and the cable could go and rest directly on the surface of the pulley. Since excavation depths can be in the order of hundreds of meters, even small percentages of elongation of the support cables can create segments of free cable of a considerable length between the spacers. These segments of free cable are not compatible with a correct sliding of the feeder lines on the transmission pulley, because for example during the rise of the tool the first spacers below the free cable segment would approach the pulley in a position that is not tangential to it, and this could cause entanglements, sticking and damages of the lines themselves, or even the impossibility of continuing the extraction maneuvers of the tool from the excavation itself.
In fact, because of the elongation of the support cables, the spacer elements are no longer guided and can rotate around the axis of the cable, being able also to assume anomalous positions. The rotation of the spacer elements can be caused by the vibrations always present during the excavation work, or by the mere moving of the drilling machine or of the tool. Generally, spacers have greater width with respect to their thickness and it is desired that during a correct winding of the lines, the lower faces of the spacer elements rest on the pulley or on the winder, in such a way as to maintain the lower contact pressure and the lower thickness of each wound layer. As a result of the rotation of one or more spacer elements, said elements could rest on the pulley or on the winder with one of their lateral faces instead of with the lower face. In this case, when the tubes are rewound, the spacers may become stuck on the transmission pulley, preventing the tubes themselves from rewinding. In the same way, a localised variation in thickness of the branch wound on the cable could be created, due to the fact that one or more rotated spacer elements are not positioned according to their minimum thickness, and this entails damages and problems when a subsequent layer of the feeder lines is deposited on this area. Moreover, as a result of the rotations, segments of free cable could be created between consecutive spacer elements, complicating, or even preventing, the retrieval operation of the tubes by means of the transmission pulley.
If a spacer is damaged during the moving of the feeder lines and is detached from the cable, all spacers positioned at a greater height thereof will tend to slide downwards, since they are axially slidable on the cable, leaving an empty space in the upper part of the branch segment. Moreover, to insert a new spacer in the branch to replace the broken one it will be necessary to disassemble the branch or the support device of the feeder lines, freeing an end of the cable to allow it to pass through the new spacer that will be added.
The technical feature described by the patent EP0518292 to reduce the problem at least partially is that of axially fastening the crossbars to the support cables, so that the total elongation of the cables is subdivided and distributed in partial elongations between one crossbar and the other. In this way, as a result of the elongation of the cables, the spacers that are between two successive crossbars can slide downward only up to the lower crossbar, leaving a segment of cable free below the upper crossbar. In this way, instead of having a single large segment of free cable below the pulley, there will be a multiplicity of segments of free cable, one below each crossbar. This feature, therefore, does not eliminate the elongation but distributes it, leaving segments of free cable between the spacers that can still be wider than a spacer, and hence cause anyway entanglements and sticking during the moving of the lines. Moreover, such a locking of the crossbars to the cables obligates to fasten the crossbars to the tubes allowing a certain degree of freedom, in order not to transmit the elongations to the tubes or cables as well, but this degree of freedom inevitably reduced the guiding function of the crossbars.
U.S. Pat. No. 7,845,154 discloses an apparatus able to guide and support the weight of a set of tubes for feeder lines, formed by two lateral support branches, connected by bars transverse to the tubes, which are held at the desired distance by a series of spacer elements interposed between them. Each spacer element is traversed by at least a pair of cables, and it is axially slidable with respect to said cables.
This patent aims to solve the problem of the rotation of the spacer elements when the cable is wound on the drum, or when the branch is suspended vertically along the excavation. To overcome this problem, into each branch is inserted a second cable of smaller diameter in an appropriate hollow housing in order to prevent the elements from rotating. This second cable, due to its sole anti-rotation function, is thinner and less rigid than the main cable, not bearing any suspension or support load.
In this case, an additional problem of alignment and distancing of the spacer elements emerges, due to the fact that under the great weight of the tubes and of all hanging parts, the two cables will absorb axial loads in different way in light of their different rigidity. In particular, the supporting cable will bear the load leaving the second cable, with smaller diameter, unloaded.
The maximum elongations which the two cables will undergo will nonetheless be associated only to those of the supporting cable.
In the situation of elongation of the supporting cables, the second cable, with smaller diameter, is unloaded, allowing the spacer elements to rotate around the hole corresponding to the axis of the supporting cable.
Moreover, since the spacers are axially slidable along the cables, the solution does not solve the aforementioned problem of the downward stacking of all the spacers present in the supporting branches when the cables are elongated under the effect of the load.
To reduce the problem of the elongation of the cables in the support devices of the feeder lines, a generally used solution is to pre-tension the cables during the mounting step of the devices. This requires one end of the cable to be fastened whilst the other is pulled until an elongation of the cable is obtained, and in this condition the spacers and the crossbars are installed. During this step, the bars will be locked to the cables so that, once the ends are released, said cables do not return to the initial undeformed condition but maintain a certain preloading compressing the spacers inserted between the crossbars. In this way, when an external load is applied to the support apparatus, the cables have smaller elongations. However, this solution has the disadvantage of requiring specific equipment to mount and pre-tension the support cables, therefore such an operation can only be carried out in a workshop and it is impossible on a construction site. Moreover, after a certain number of work cycles the elongations return, hence means for restoring the tensioning are provided. These means can be, for example, wedge elements to be forcibly inserted between the spacers to induce an axial load along the cable. Therefore, this system has the limitation of requiring frequent checks and maintenance to maintain its effectiveness. Moreover, if a spacer breaks and is disengaged from the cable, in the corresponding branch segment there will be a reduction of the size of the elements interposed between two crossbars, and thus such crossbars will tend to approach each other, eliminating the preloading present on the cable.
A hypothetical solution to eliminate the problem of the elongation of the cable suspension elements, would be to replace them, for example, with chains that develop in length in extended configuration along a longitudinal development direction and although they allow lateral flexions, they are extremely stiffer in the longitudinal direction and hence they have altogether negligible elongations for these applications.
Known articulated chains, e.g. the Galle or the Fleyer chains type, are made of links consisting of a plurality of platelets each of which has elongated shape in the direction of longitudinal development of the chain, and small thickness. These platelets are connected to each other through pins transverse to the direction of longitudinal development of the chain, forming the links. These links can, therefore, rotate relative to one another around the axes of the pins and allow the chain to be wound. By fastening several platelets arranged side by side in parallel on each pin, compact and very stiff chains can be obtained, with high strength capacities. In order for these chains to work correctly, the platelets must be mounted with precise couplings on the pins, because excessive clearances would lead to a rapid wear of the chain. These chains cannot be used in devices for the excavation of diaphragms because if they are immersed into the stabilizing fluids of the excavations, in contact with these fluids they tend to seize, losing the indispensable flexibility to allow winding on drums. Stabilizing fluids, which are generally bentonite-based, are highly basic and cause a rapid oxidation of the chains, and this oxidation can cause the pins of the links to lock, preventing the rotation of a link relative to the other. This oxidizing and corrosive effect is amplified if the chain is cyclically first immersed and then let dry in air.
Ring chains, also called Genoa chains, consist of a sequence of rings that intersect each other in such a way as to allow a limited movement of each ring relative to the others in the direction of longitudinal development of the chain. Each ring is mounted rotated by ninety degrees relative to the preceding one around the longitudinal axis of the chain. This type of chain has high tensile strength and is also very flexible in all directions. The absence of a constraint that obligates the rings to rotate on a given plane allows extreme freedom of relative movement between the rings and the chain can thus flex on any plane. In addition, each ring can effect relative rotations with respect to the preceding ring and to the following ring around the longitudinal axis of the chain. This latter characteristic makes it problematic to use ring chains in known support and guiding devices of the feeder lines for excavation devices. In fact, using a ring chain in support and guiding devices of the feeder lines, the spacer elements connected to the chains would tend to rotate around the axis of the chains themselves, making a correct orientation of said elements difficult. Moreover, both articulated chains and ring chains are unsuitable to be wound in an orderly manner on several layers around a drum. Since they do not have specifically provided support surfaces and guiding elements, they would tend to misalign and to tangle with respect to the lower layers. More in particular, ring chains have no flat surfaces suitable to the orderly superposition of the coils and during winding it is possible for the rings, as they progressively superposed in different layers on the drum, tend to mutually rotate around the longitudinal axis of the chain, causing misalignments of the layers with possible entanglements.